The present invention relates to thermoplastic bags useful for packaging bread and other food products and, in particular, metallized thermoplastic bags useful for packaging such products on high speed automatic loading equipment.
The food industry has used thermoplastic bags to package bread and other products for many years. Typically, these bags are formed of some blend of polyethylene or similar polymers and are advantageous in maintaining freshness as well as allowing the consumer to view the product. In many, if not most cases, these bags are manufactured from rolls of continuous film which is folded and heat sealed to form the desired bag product. Commonly, the resulting bags will have an open end and a closed end that contains a series of folds and heat seals which form what is known as an end gusset.
The completed bags are used by food packagers on automated high-speed loading equipment which applies high stress to the heat sealed portions of the end gusset during the loading process. In order to maintain an air-tight integrity, the heat seals must be of sufficient strength to withstand the loading stresses.
The packaging industry has often sought to increase consumer appeal for a particular product by varying the surface of the package containing the product. In the bread industry, for example, many of the thermoplastic bags used for packaging are labeled or coated in such a way as to attract consumers. Bread and other products which are contained in bags are typically placed on the store shelf with the closed or gusseted end facing the consumer. It is, therefore, desirable to coat or label the gusseted portion of these bags.
Decorative labels or coatings must be applied to the thermoplastic film prior to folding or heat sealing. The most common approach to such labeling or coating includes feeding a continuous roll of film through a surface coating process or printer where the desired design or surface coating is continuously applied.
One method of coating known as metallization involves applying a metallized surface to the thermoplastic film. Aluminum can be deposited on the surface of the film in a continuous sheet or strip which runs along the entire length of the film. The metal must be deposited in a unidirectional process in continuous sheets or strips. Consequently, design gaps or breaks in the metallized surface cannot be directed to the film on a site-specific basis. Therefore, this application process inherently has limitations, especially when manufacturers attempt to direct the placement of a metallized surface to the portion of the bag which results in the end gusset area.
Another major problem with metallized thermoplastic film is that it tends to form weak heat seals in any areas in which two metallized film surfaces contact one another to form a seal.
Previous attempts to place a metallized surface in the end gusset area of thermoplastic bags used on automatic loading equipment have been unsuccessful because the resulting heat seals in the gusset area were not able to withstand the stress incurred during the loading operation.
It is, therefore, an object of the present invention to provide a thermoplastic bag with an end gusset having both a metallized surface and adequate heat seal strength for use on automatic packaging or loading equipment.